Federal safety requirements require vehicles to withstand loads on the vehicle roof area for occupant safety and protection. These load requirements, expressed as a percentage of vehicle weight, increase as newer Federal requirements are established. The roof load requirements are intended to simulate loads on the vehicle encountered during a vehicle rollover event. Other frame members, such as upper and lower frame rails that extend generally longitudinally on the automotive frame, also experience crushing loads from crashes that result in the collapse of the frame member. The newer, more demanding Federal requirements force countermeasures, i.e. changes to the structure of vehicle body and frame, which can ultimately add significant cost and weight to the vehicle.
It is essential to minimize the weight of the vehicle, and thus the countermeasures adopted to meet the newer Federal safety requirements, as added weight to the vehicle frame translates into increased load requirements, as the requirements are expressed in terms of a percentage of the total vehicle weight. Increasing frame size is, therefore, a “Catch 22” type of situation in that the addition of structure to meet the load requirements of the newer regulations results in increased load requirements that must be resisted by the frame structure to satisfy the Federal requirements. Thus, conventional solutions required to meet the Federal safety requirements, by adding large, heavy steel reinforcements are counterproductive. The utilization of lighter weight materials and composites can offer equivalent vehicle frame structure that will withstand the required roof loads; however, these lightweight materials are typically substantially more expensive than conventional steel components, which make the cost of the vehicle frame prohibitively expensive and would render the vehicle commercially uncompetitive.
When the vehicle frame components are loaded through the roof, the vehicle body pillars and rail cross-sections achieve a peak loading and then proceed to collapse. In the process of collapsing, the frame cross-section changes geometric shape into a less stable cross-sectional profile. The progressing geometric shape change continues until the load carrying capability of the structural frame member is reduced below the buckling threshold, where collapse occurs.
The conventional approach to increasing the load carrying capacity of a vehicle structural frame member can be seen in U.S. Pat. No. 6,328,376, issued to Baik-Lark Son on Dec. 11, 2001, in which a reinforcing member that cooperates with a stepped portion of the reinforcing panel in a manner to delimit the closed space and increase the overall rigidity of the center pillar. Similarly, a reinforcing panel is added to the vehicle structural frame member formed from two hat-shaped components to increase the weight and the section of the structural member in U.S. Pat. No. 6,397,553, granted to Tooru Horikawa, et al on Jun. 4, 2002.
A reinforcement for a vehicle roof rail and center pillar is placed between the inner and outer panels of the structural member as taught in U.S. Pat. No. 6,705,668, issued on Mar. 16, 2004, to Masashi Makita, et al by welding flanges of the reinforcement member and inner and outer panels to each other, thus increasing vehicle rigidity. In U.S. Pat. No. 6,917,654, granted on Nov. 16, 2004, to Yuichi Kitagawa, et al, a pillar reinforcement panel has flanges that are pinched and welded between corresponding flange parts of inner and outer pillar pieces to increase pillar rigidity.
U.S. Pat. No. 6,988,763, issued on Jan. 24, 2006, to Hidetsugu Saeki, et al discloses a U-shaped energy absorbing section welded to the outside of a center roof pillar to provide structural integrity such that other members are deformed only after the energy absorbing section has completely deformed due to impact loading. The U-shaped reinforcement member can be welded to the inside surface of the outer pillar panel to provide an impact absorbing member. In U. S. Patent Application Publication No. 2005/0212326, by Thomas Marion, dated Sep. 29, 2005, a reinforcement member has three pivotable walls positioned within the vehicle structure defining a cavity, such as a roof assembly or a roof pillar in a vehicle.
It would be desirable to provide a stability device in a vehicle structural frame member that is operable to retain the geometric cross-sectional shape of the frame member while undergoing crash loading.